AGRON / MTEOR 404Global Change

Changes to Water Resources

Raymond Arritt

Department of Agronomy

Effects of water resources

• erosion• Timing in crop growth cycle• Runoff – wastewater treatment, pollution• Groundwater depletion, subsidence• Distribution of rainfall, shifting patterns• Hydropower (energy)• Distribution of ecosystems; desertification

• Effect on flood plains

• Water ownership – who gets to use it?

• Ecology and biodiversity – new species introduced, take over and lose diversity

• Shift in rainfall patterns (wet and dry regions)

• Sustainable development – building

• Irrigation systems – change in demand• Energy production – cooling water for

powerplants and industry• Water conservation awareness• Snowmaking for ski areas• Dams and storage• Glaciers• How do we get people to understand?

IPCC Fourth Assessment Report Summary for Policy Makers

A simple surface water budget

Precipitation – Evaporation = Runoff + Storage

storage includes lots of things:

soil moisture, aquifers, reservoirs, withdrawals for irrigation, glaciers, snowpack, etc.

IPCC Fourth Assessment Report Summary for Policy Makers

Change in annual runoff

2041-2060 compared to 1900-1970

Where do we see increases in runoff?Where do we see decreases?

Predicted changes in groundwater recharge

Some observed effects on water resources

Predicted effects of climate change on water resources

Fastest growing states

Water resource stress without climate change

Current

2055 (IPCC A2 scenario)

Change in water resource stress with climate change

reduced water stress in tropical regionsincreased water stress

outside the tropics

results from two different climate models

What is drought?

• One definition:

• Elements of the definition:– deficiency of precipitation– extended period (how long is "extended"?)– water shortage for some user ("group or activity")

A deficiency of precipitation over an extended period that causes water shortage for some group or activity.

Drought depends on the user

• Crops rely on stored soil water. Soil water can be rapidly depleted, so that monthly droughts may affect crops.

Drought depends on the user

• Rivers and streams may dry out during seasonal droughts.

Arnie! I found your keys!

Drought depends on the user

• Multi-year droughts may deplete ground water that supports communities.

Drought, more precisely

• Must define the time period over which precipitation is below normal.

• Must define what is a water shortage that affects a particular activity.

Iowa corn yields

1988 drought 1993 flood

Remember

• Changes to water resources depend on more than just the change in rainfall.

• Whether a change is good, bad, or neutral depends on who we are and what we’re interested in.